1. Field
Embodiments of the present disclosure relate to a thermoelectric element having improved thermoelectric efficiency and a method of manufacturing the same.
2. Background
A thermoelectric effect means a reversible, direct energy conversion generated between heat and electricity and is generated by electron and hole transfer performed in the inside of a material. Such a thermoelectric effect is divided into a Peltier effect and a Seebeck effect, the Peltier effect being applied to the cooling field using a temperature difference in both ends formed by a current applied from the outside, and the Seebeck effect being applied to the power generation field using an electromotive force generated due to the temperature difference in both ends of the material.
The biggest factor to limit the application of thermoelectric cooling and power generation is the low energy conversion efficiency of a material. The performance of a thermoelectric material is commonly called the dimensionless figure of merit. A value of the figure of merit ZT defined by the following Equation is used.
                    ZT        =                                            S              2                        ⁢            σ            ⁢                                                  ⁢            T                    κ                                    [                  Equation          ⁢                                          ⁢          1                ]            
Here, ZT represents the figure of merit, S represents a Seebeck coefficient, σ represents electric conductivity, T represents an absolute temperature, and κ is thermal conductivity.
However, electrical conductivity and a Seebeck coefficient have a correlation in which when performance of one of them is increased, performance of another one is decreased. Thus, as shown in Equation 1, in order to increase the figure of merit of a thermoelectric material, researches for increasing a Seebeck coefficient and electrical conductivity and reducing thermal conductivity have been performed.
As one example of technologies resulting from these researches, a conventional cooling thermoelectric element has been mainly produced in a bulk type. However, since the bulk-type thermoelectric element has a small scattering effect of phonons, it has the low figure of merit. Thus, improvement has been needed for the bulk-type thermoelectric element.
Also, as shown in Equation 1, electrical Conductivity and the Seebeck coefficient corresponding to main variables determining the ZT value have a correlation in which when performance of any one of them is increased, performance of another one is decreased. Thus, even though thermal conductivity is decreased when the Seebeck coefficient is increased according to a decrease of the concentration of a carrier, a trade off property showing the decrease of an electrical conductivity property is generated.
The conventional bulk-type thermoelectric element has a low competitive price because it is based on Bi—Te. Thus, the conventional bulk-type thermoelectric element has been only used in limited fields such as expensive equipment or the aerospace industry. Also, since the conventional bulk-type thermoelectric element has no flexibility, it cannot be used in a surface with curvature. Thus, it is difficult to variously utilize it. Accordingly, the development of a thermoelectric having a competitive price and a flexible property has been necessarily needed.